Heterogeneous deformation and damage mechanisms in multiphase Mg-Li alloys: In-situ XCT and coupled CPFE-PF analysis

In material design, preventing crack propagation is crucial for improving structural reliability and extending service life. Here, we report a new phenomenon where the soft β-Li phase in Mg alloys coexists with the hard α-Mg phase, and very hard Al₂RE precipitates form at the interface between the β-Li and α-Mg phases, exhibiting a multiphase heterogeneous microstructure. By using X-ray tomography, we have observed the arresting of cracks at the β-Li/a-Mg interface and cracking is only allowed along the very hard Al₂RE precipitates, increasing the strength and ductility of the three-phase alloy significantly. From atomistic molecular dynamic simulation, three-phase alloys enhance strain hardening through {112} dislocation slip mechanisms, which create barriers to crack propagation. In-situ observation and crystal plasticity finite element coupled with phase field (CPFE-PF) have shown that most cracks are arrested by the interconnected β-Li phase network, and cracks have to propagate along the tortuous paths, limiting their mobility. Therefore, this finding lays the foundation for high ductility and durability design of Mg alloy by arresting the initial cracks in their diversifying soft/hard neighboring cells.